Scanning focal plane sensor systems and methods for imaging large dynamic range scenes

ABSTRACT

A scanning focal plane sensor and method are described for image capturing of object space (or scenes). In one example, a focal plane sensor for a scanning imaging system is provided. The focal plane sensor for a scanning imaging system includes M×N Time Delay Integration (TDI) imaging Charge Coupled Device (CCD), where M is a number of TDI columns and N is a number of TDI stages per each column. A detector is connected to each TDI stage. The focal plane sensor includes an imaging controller configured to mechanize sampling the brightness value of each sensor pixel&#39;s initial footprint in object space and select a number of charge integrating TDI stages for substantially equalizing the inter sensor pixels&#39; signal to noise ratios.

TECHNICAL FIELD

The present invention relates to focal plane sensors, and moreparticularly to systems and methods for imaging large dynamic rangescenes via scanning focal plane sensors.

BACKGROUND

Scanning Imaging systems have focal plane sensors operating in differentspectral bands (for example, Ultraviolet (UV), or Visible, or ShortWavelength Infrared (SWIR), or Mid Wavelength Infrared (MWIR), or LongWavelength Infrared (LWIR)) that have difficulty imaging scenes withlarge dynamic range. Object space, or scene, are imaged with focal planesensors which contain many sensor pixels, where each sensor pixelconsists of a photodetector with readout provisions. Focal plane sensorsimage a scene by virtually dividing it into small areas where each smallarea is the footprint of a sensor pixel in object space (or the scene).Large dynamic range scenes contain regions which when imaged with sensorpixels will exhibit very large, or average, or very low photosignals.Characteristically, imaging such scenes has three problems: (i) sensorpixel's overexposure, or underexposure, (ii) digitization of largedynamic range signals (>15 bits), and (iii) poor sensitivity inoverexposed or underexposed sensor pixels. Adjusting globally theintegration time to optimize the image according the average scenebrightness is not an adequate solution for imaging large dynamic rangescenes. The average brightness approach is utilized for film imaging,and is most effective for low dynamic range scenes, but inadequate forimaging large dynamic range scenes.

Recently, another approach has been introduced for imaging high dynamicrange scenes which combines multiple images, each taken at a differentexposure. Multiple images are merged with a software program into asingle combined image. The combined image merges dim image regions(acquired with the longest exposure) with average brightness imageregions (acquired with intermediate exposure) with very bright imageregions (acquired with short exposure). Software is used to selectssensor pixels with the best exposure (signal to noise ratio) and afterproper scaling, the software combines the selected sensor pixels into asingle surreal image. The combined image produced from multipleexposures and post processing can be effective for imaging large dynamicrange scenes, however, it has serious drawbacks. First, multiple imagesrequire more time and are appropriate for slow scenes, and not fasterscenes. Second, combining multiple images requires sensor pixel tosensor pixel registering in multiple images, otherwise blurring willoccur. These additional requirements limit the utility of the multipleimage approach to situation where: (1) a tripod is used for goodstability between the camera and scene, and (2) the scene does notchange rapidly.

The problem of imaging large dynamic range scenes is illustrated by theexample in TABLE 1. The scene's dynamic range entered in the secondcolumn is divided into five subranges. Such division illustrates severalcharacteristics of imaging with focal plane sensors containing quantumphotodetectors with readout provisions. First, signals from largedynamic range scenes have photosignals which vary over a wide dynamicrange (see column 2 in TABLE 1) and the signal to noise ratio variesaccording to Poisson statistics as the square root of the signal (seecolumn 3 in TABLE 1). Poor sensitivity occurs because the S/N decreasesmonotonically as the square root of the signal. At the highest signallevels, sensor pixel saturation can occur and lead to poor sensitivity.Second, sensitivity dependence of a sensor pixel's photosignalcomplicates digitizing signals from large dynamic range scenes.Typically, an analog-to-digital (A/D) convertor's least significant bit(LSB) is adjusted to equal approximately the signal's noise level. It isdifficult to define a global LSB value for an imaging focal plane sensorbecause each sensor pixel's noise varies with photosignal (see column 3in TABLE 1). This would require varying the A/D LSB for each range (seecolumn 5 in TABLE 1) which raises many complications.

Conventionally, the A/D converters LSB is set at the minimum noise leveland that causes inefficient A/D converter operation since significanttime is consumed digitizing noise. Third, in large dynamic range imagesthe signal-to-noise (S/N) ratio is maximum in scene regions with highphotosignals and minimum in regions with low photosignals (see column 4in TABLE 1). This effect translates into noticeable variation in imagequality wherein the best (poorest) image quality is in regions where thesensor pixels have high (low) level photosignal.

TABLE 1 below is an example of the signal levels expected in focal planesensors with quantum photodetectors. Each sensor pixel is subjected tothe same integration time and field of view. After one integration time,the integrated charge photosignal in each sensor pixel is assumed tovary between 12 and 12,500 photoelectrons. The signals dynamic range hasbeen divided into five subranges to illustrate how a sensor pixel'snoise and S/N ratio varies with signal (see, respectively, third andfourth columns). Digitizing signals with different noise levelscomplicates selecting an optimal value for the A/D converter's LSBvalue.

TABLE I Unsealed Instantaneous A/D Signal Un-scaled Un-scaled S/N (#Bits) Converter Range Signal Range Noise Range Before LSB # (electrons)(electrons Scaling (electrons) 1  3,125-12,500  56-112 <8 30 2  782-3,125 28-56 <6 15 3 196-782 14-28 <5 7 4  49-196  6-14 <4 3 512-49 3-7 <3 1.5

SUMMARY

In accordance with one example, a focal plane sensor for a scanningimaging system is provided. The focal plane sensor for a scanningimaging system includes M×N Time Delay Integration (TDI) imaging ChargeCoupled Device (CCD), where M is a number of TDI columns and N is anumber of TDI stages per each column. A detector is connected to eachTDI stage. The focal plane sensor includes an imaging controllerconfigured to mechanize sampling the brightness value of each sensorpixel's initial footprint in object space and select a number of chargeintegrating TDI stages for substantially equalizing the inter sensorpixels' signal to noise ratios.

In accordance with another example, the focal plane sensor is configuredto perform imaging with forward and a reverse scan operation. The focalplane sensor comprises a bidirectional M×N TDI imaging CCD, where M is anumber of TDI columns and each column has N TDI stages. Each TDI stageis connected to a detector and each sensor pixel's signal canselectively be increased by up to N TDI integrations. The focal planesensor further comprises M×K sensing stages, where K is an integergreater than one, wherein a first set of sensing stages for each of theM sensor pixels resides on a first side of the bidirectional M×N TDIimaging CCD and a second set of M×K sensing stages for each of the Msensor pixels resides on a second side of the bidirectional M×N TDIimaging CCD, and an imaging controller configured to determine aninitial photosignal brightness value for each sensor pixel based on aninitial image capture with the first set of M×K sensing stages during aforward scan, and to determine an initial photosignal brightness valuefor each sensor pixel based on an initial image capture with the secondM×K sensing stages during a reverse scan. The imaging controller selectsa number of charge integrating TDI stages applied for each respectivesensor pixel based on its respective initial photosignal brightnessvalue.

In yet a further example, a method is provided for image capturing froman object scene by a scanning focal plane sensor. The method comprisesdetermining an initial photosignal brightness value for each of aplurality of sensor pixels based on an initial capture of an image froman object scene, and utilizes each sensor signal's initial photosignalbrightness value to determining an integration TDI scale factor. Theintegration TDI scale factor for each sensor pixel is based on thesensor pixel's brightness value and within which predetermined sensorpixel signal range it occupies. The integration TDI scale factor appliedto each sensor pixel equalizes the inter sensor pixels' signal to noiseapproximately within a factor of 2.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of a functional block diagram of a focalplane sensor in a scanning imaging system.

FIG. 2 illustrates an example of method for image capturing of an objectscene by a focal plane sensor in a scanning imaging system.

FIG. 3 illustrates an example functional block diagram of an A/Dconverter and digital unscaling stage.

FIG. 4 shows a block diagram of an example register illustratingoperations of a digital unscaling arithmetic unit.

FIG. 5 illustrates an example of a TDI column with sensing stages atboth ends and which are used to detect each sensor pixel's brightnesswhen imaging an object space (or scene) with a focal plane sensor.

FIG. 6 illustrates another example of a TDI column with 4-TDI sensingstages on the left and right sides of the Read/Outs and which are usedto detect each sensor pixel's brightness when imaging object space (orscene) with scanning focal plane sensor.

FIG. 7 illustrates an example of a sensor pixel's block diagram with afour phase TDI-CCD clocking cell, the detector is left out for clarity.

FIG. 8 illustrates an example of a hybrid assembly of scanning focalplane sensor for a scanning imaging system.

FIG. 9 illustrates another example of a hybrid assembly of a scanningfocal plane sensor for a scanning imaging system.

DETAILED DESCRIPTION

The present disclosure provides a focal plane sensor architecture forscanning imaging systems and methods for imaging large dynamic rangescenes, and providing images with substantially equalized inter sensorpixel signal to noise (S/N) ratios (e.g., within approximately 2×)irrespective of the brightness value of each sensor pixel's footprint inobject space. This is accomplished by applying a digital transformationto each sensor pixel's photosignal to substantially equalize each sensorpixel's photosignal within a same brightness range and S/N ratio. Thedigital transformation adjusts each sensor pixel's integration time by ascaling factor which depends on a sensor pixel's initial photosignalbrightness thereby scaling each sensor pixel's photosignal into apredetermined sensor pixel signal range. This substantially equalizesthe S/N ratio of each sensor pixel's photosignal value to withinapproximately 2× of one another. Based on the scaling factor, eachsensor pixel's integration time is adjusted by selecting a number of TDIstages it receives. The scaled sensor pixel value is then converted fromthe analog to the digital signal, thus capturing the optimized S/N ratiofor each sensor pixel. The digital scaled sensor pixel value is thendigitally unscaled by its respective scaling factor to recover thesensor pixel's original brightness signal while maintaining thedigitally captured and equalized inter pixels S/N ratio.

The aforementioned digital transformation invented for high dynamicrange imaging governs the operation and digitization of each sensorpixel in the focal plane sensor. This digital transformation satisfiestwo very important constraints: (1) Each sensor pixel's output signalvalue (neglecting global gain factors and quantization errors) remainsunchanged, and (2) scaling equalizes the inter sensor pixels' signal tonoise ratios approximately to within 2×. The first constraint insuresthat the digital transformation does not distort the image. Hence,unscaling is performed as part of digital transformation to recover andobtain a digital representation of each sensor pixel's initialphotosignal value (neglecting global gain factors). This does notpreclude using compression algorithms to process the high dynamic rangedigital images for displaying on limited dynamic range displays. Thesecond constraint equalizes (within approximately 2×) inter sensorpixels' sensitivity and thereby insures optimal S/N ratios in sensorpixels with small, average, and large photosignals.

To maximize scan efficiency, a focal plane sensor is configured toimplement bidirectional scan over an array of TDI imaging CCD columns.Each TDI imaging CCD column provides signal enhancement by operating ina time delay and integrate (TDI) mode. In this mode, the scanned imagemoves synchronously with the analog photosignal physically shiftedinside the CCD channel. Synchronized movement of image and chargesignals within the TDI-CCD channel results in build-up of thephotocharge signal in the TDI-CCD channel. Photocharge signal buildupdepends on the number of TDI stages applied in the TDI-CCD imagingcolumn. This invention teaches how to vary the number of TDI-CCD stageswithin a TDI column used for building up of the photocharge signal.

For example, a CCD imaging column with 10 TDI stages can build up thephotocharge signal by 10× over what a single TDI stage would collect.Thus in a scanning focal plane sensor with N TDI stages, the maximumeffective integration time (N*TINT) depends on the product of: (1) thescanning speed of the image over the imaging TDI-CCD column (related toTINT), and (2) the number “N” which representing the number of TDIstages used to built up the photosignal in a TDI-CCD imaging column. Inconventional scanning focal plane sensors the number of TDI stages canonly be globally selected where every sensor pixel in the focal planearray is buildup by the same number of TDI stages per sensor pixel.

In accordance with an aspect of the present invention, a focal planesensor/method is provided that provides advanced knowledge of eachsensor pixel's photosignal value since this information is needed todetermine the optimal number of TDI stages that should be applied toeach sensor pixel. Additionally, a structure/method is illustrated foradjusting, in a N offstage TDI column, the effective integration timeper sensor pixel by varying the number of TDI stages applied per pixel.

FIG. 1 illustrates an example of a functional block diagram of ascanning focal plane sensor for an imaging system 10. The scanning focalplane sensor for an imaging system 10 includes an imaging controller 12configured to control the focal plane sensor for the scanning imagingsystem's 10 and includes provisions for capturing and processing eachsensor pixel's brightness footprint in object space (scene). The focalplane sensor for the scanning image system 10 includes bidirectional M×NTDI imaging CCD 14 comprised of M TDI columns, with N TDI stages in eachTDI Column. Each TDI stage is connected to a detector and the number ofTDI stages applied to each sensor pixel is adjustable up to a maximum ofN TDI stages.

Hybrid focal plane sensors have the sensor pixels wherein the pixel'sdetector is made in a separate semiconductor crystals than the pixel'sreadout stage, and this architecture is illustrated in FIG. 7 withoutillustrating the sensor pixel's detector. Each sensor pixel's TDI stageincludes a DI Source for connection to a pixel's detector for acceptingphotogenerated signals and injecting these into an Integration Welllocated in the TDI cell. Photogenerated charges from the integrationwell are moved into a TDI-CCD well for transport with and aggregationunder the TDI-CCD clocking gates. Movements of signal charges from thepixel's detector into the Integration Well, the Blooming Drain, and theTDI-CCD well, are controlled by the imaging controller 12 via operatingand address signals.

The imaging system 10 with the focal plane sensor can include aninput/output device 16 that receives image results from the imagingcontroller 12 and displays them. The input/output device 16 can alsoprovide synchronization inputs of the imaging system platform relativeto the object scene, such as height, distance, speed or other parametersfor synchronizing movement of projected object space images along TDIstages with movement of photogenerated image signals within the TDI-CCDcolumns. Movement synchronization between object space images movingalong TDI stages with movement of photogenerated image signals withinthe TDI-CCD is mechanized for moving or stationary systems usingscanning focal plane sensor controlled by the imaging controller 12.

A first parallel in/serial out (PI/SO) CCD multiplexer 18 resides on afirst side of the TDI Imaging CCD 14 and a second PI/SO CCD multiplexer24 resides on a second side of the TDI Imaging CCD 14. A plurality offorward scanning M×K TDI sensing stages 20 reside adjacent to the firstPI/SO 18 and a plurality of backward scanning M×K TDI sensing stages 26reside adjacent the second PI/SO CCD multiplexer 24. The forwardscanning M×K TDI sensing stages 20 provide the imaging controller 12advanced knowledge of each sensor pixel's object space footprintphotosignal brightness during a forward scan, where K is an integergreater than one. This information is used to determine how many TDIstages are applied to each sensor pixel while being imaged with the M×NTDI imaging CCD during a forward scan. The reverse scanning M×K TDIsensing stages 26 provide the imaging controller 12 advanced knowledgeof each sensor pixel's object space footprint photosignal brightnessduring a reverse scan. This information is used to determine how manyTDI stages are applied to each sensor pixel during a reverse scan.

In forward scan, the photogenerated charge signals from the FS M×K TDIsensing stages 20 are multiplexed by the first PI/SO CCD multiplexer 18to a first read out circuit 30, which converts the photogenerated chargesignals to an analog voltage. The analog voltage signals are digitizedwith an A/D converter and the digital outputs are digitally unscaled instage 32 according to inputs from controller 12 which contains the K TDIscaling information applied to each pixel in the sensing stage 20. Theimaging controller 12 also synchronously provides to FS M×H DBD controlcircuits 28 scaling information on the number of TDI stages each sensorpixel receives and this is implemented with digital blooming drains(DBD) located inside the bidirectional M×N TDI Imaging CCD. The DBDinside the bidirectional M×N TDI Imaging CCD are controlled and addresswith the FS M×H DBD control circuit 28, where H is an integer greaterthan one.

The scaled analog sensor pixel values from the bidirectional M×N TDIImaging CCD 14 are multiplexed with the second PI/SO CCD multiplexer 24to a second read out circuit 34, which converts the photogeneratedcharge signals into analog voltages. The analog voltages are digitizedwith an A/D converter and digitally unscaled with stage 36. Digitalunscaling recovers a digital equivalent of each sensor pixel's footprintbrightness signal in the object space and maintains the improved intersensor pixels' equalized S/N ratios, approximately within 2×. The finalimage with equalized inter sensor pixels S/N ratios (within 2×, forexample) is then provided to the input/output device 16, for example, tobe displayed.

In reverse scan, photogenerated charge signals from the RS M×K sensingstages 26 are multiplexed by the second PI/SO CCD multiplexer 24 to thesecond read out circuit 34, which converts the photogenerated chargesignals to an analog voltage. The analog voltage signals are digitizedwith an A/D converter and the digital outputs are digitally unscaledwith stage 36 according to inputs from controller 12 advanced whichcontains the K TDI scaling information applied to each pixel in thesensing stage 26. The imaging controller 12 also synchronously providesto RS M×H DBD control circuit 22 scaling information on the number ofTDI stages each sensor pixel receives and this is implemented withdigital blooming drains (DBD) located inside the bidirectional M×N TDIImaging CCD. The DBD inside the bidirectional M×N TDI IMAGING CCD arecontrolled and addressed with the RS M×H DBD control circuit 22, where His an integer greater than one.

The scaled sensor pixel values from the bidirectional M×N TDI ImagingCCD 14 are multiplexed with the first PI/SO CCD multiplexer 18 to thefirst read out circuit 30, which converts the photogenerated chargesignals into analog voltages. The analog voltages are then digitized byan A/D converter and digitally unscaled with stage 32. Digital unscalingrecovers a digital equivalent of each sensor pixel's footprintbrightness signal in object space and maintains the improved intersensor pixels' equalized S/N ratios, approximately within 2×. The finalimage with equalized inter sensor pixel S/N ratios (within 2×, forexample) is then provided to the input/output device 16, for example, tobe displayed.

FIG. 2 illustrates a method example for capturing an image of objectspace (or scene) with a focal plane sensor for a scanning imagingsystem. The methodology begins at 42 where initial photosignalbrightness values are determined for each of a plurality of sensorpixels by an initial sample of each sensor pixel's footprint brightnessin object space, or scene. At 44, a scale factor is determined for eachsensor pixel to equalize the inter sensor pixels' signal to noise ratioswithin 2× (approximately). Inter sensor pixels signal to noise ratiosequalization is performed by scaling (or adjusting) each sensor pixel'sintegration time. For each sensor pixel the scale factor is determinedfrom which signal range each sensor pixel's photosignal value occupies.Each sensor pixel's integration time is scaled by adjusting the numberof TDI stages applied to a sensor pixel at 46. Scaling the number of TDIper sensor pixel equalize the inter sensor pixels' S/N ratios within afactor of 2×, approximately. At 48, each of the plurality of the sensorpixels' scaled photogenerated analog charge signals are converted toscaled analog voltages. At 50, the scaled analog voltages are digitizedto provide scaled digital pixel values, and capturing the equalized(within 2×, approximately) inter pixels signal to noise ratios. At 52,each scaled digitized scaled pixel value is digitally unscaled torecover each sensors pixel's initial photosignal brightness value.

In accordance with one example, five signal ranges have been assigned tosensor pixels' signal values that span from 12 electrons, for thedimmest signals, up to 12,500 electrons, for the brightest signals. Eachsignal, falling within one of the four lower level signal ranges, isscaled up by variable integration time per pixel into the highest(brightest) sensor pixel signal range. Accordingly, the integration timeis increased by varying the number of TDI stages applied to each sensorpixel to correspond to the scaling factors illustrated in TABLE 2 below.

TABLE 2 4T_(INT) 16T_(INT) 64T_(INT) 256T_(INT) Pixel's Pixel's Pixel'sSignal Signal Signal Signal Signal Signal Range Noise Range Pixel'sScaling Scaling Scaling Scaling Range electrons) (electrons) S/N Ratio(electrons) (electrons) (electrons) (electrons) 1  3,125-12,500  56-112 56-112 (7 Bits) 12.5k-50k    50k-200k 200k-800k 800k-3.2M 2   782-3,12528-56 28-56 (6 Bits) 3.125k-12.5k  12.5k-50k    50k-200k 200k-800k 3196-782 14-28 14-28 (5 Bits)    782-3.125k 3.125k-12.5k  12.5k-50k   50k-200k 4  49-196  6-14  6-14 (4 Bits) 196-782    782-3.125k3.125k-12.5k  12.5k-50k   5 12-49 3-7 3-7 (3 Bits)  48-196 196-782   782-3.125k 3.125k-12.5k 

The first four columns in TABLE 2 correspond to the first four columnsin TABLE 1, and all entries are calculated for the same integration timeTINT, which corresponds to a 1× scaling. Columns 5, 6, 7, and 8 havebeen calculated assuming a sensor pixel's integration time was scaled,respectively, by 4×, 16×, 64× and 256×. Each one of the five SignalRanges in column 2 can be equalized to Signal Range #1 by using theproper scaling factor: Signal Range #2 is scaled by 4×, Signal Range #3is scaled by 16×, Signal Range #4 is scaled by 64×, and Signal Range #5is scaled by 256×. Such scaling maps all signals into Signal Range #1and thereby equalizes all the sensor pixels' S/N ratio withinapproximately 2×.

In TABLE 2, columns 5, 6, 7, and 8 have been calculated for scaling asensor pixel's integration time by 4×, 16×, 64× and 256, respectively.Arbitrary scaling a sensor pixel's integration time can lead tosaturation. Scaling all sensor pixels' into Signal Range 1 by 16× willresult in saturation sensor some sensor pixels. Similarly, scalingsensor pixels in Signal Range 2 (3) by 64× (256×) will also result insensor pixel saturation. However by selectively applying differentscaling to each the five Signal Ranges listed in TABLE 2 map all thesignals into Signal Range #1 and thereby equalizes the inter sensorpixels' S/N ratio in all the 5 Signal Ranges. Such a mapping isperformed by scaling the four lower Signal Ranges (#2, #3, #4 & #5) by(4×, 16×, 64×, and 256×), respectively, into the Signal Range #1. Such amapping is shown in TABLE 3, column 6 below.

TABLE 3 Instantaneous Scaled Scaled A/D Un-scaled Un-scaled S/N (# Bits)Linear Signal Converter Signal Signal Range Noise Range Before ScaleRange Instantaneous LSB Range (electrons) (electrons) Scaling Factor(electrons) S/N (# Bits) (electrons) 1  3,125-12,500  56-112 <8   1X3,125-12,500 <9 30 2   782-3,125 28-56 <6   4X 3,125-12,500 <9 30 3196-782 14-28 <5  16X 3,125-12,500 <9 30 4  49-196  6-14 <4  64X3,125-12,500 <9 30 5 12-49 3-7 <3 256X  3125-12,500 <9 30

The digital transformation maps five Signal Ranges (column 2, TABLE 3)into a single range between 3,125 and 12,500 electrons (column 6, TABLE3). This accomplishes two very important things: it equalizes the S/Nratio for all sensor pixels to within approximately 2×, and greatlysimplifies A/D conversion by equalizing the LSB (see column 8, TABLE 3).Equalization is achieved with scaling which adjusts each sensor pixel'sintegration time to map all the five Signal Ranges into one rangebetween 3,125 and 12,500 electrons. Since each sensor pixel's signalobeys Poisson statistics, the mappings equalizes the signal-to noiseratio within the five Signal-to-Noise ratios scene regions. Equalizingthe inter sensor pixels' S/N ratios results in bright, average, and dimsensor pixels with the same S/N ratios, approximately within 2×.Furthermore, scaling simplifies digitization of sensor pixels' signalsfrom large dynamic range scenes.

As previously stated, the digital transformation technique allows forutilization of an A/D converter with less bits compared to the number ofbits needed without employing the digital transformation technique. FIG.3 illustrates an example functional block diagram of an A/D converterand digital unscaling stage with five sensor pixel signal ranges asillustrated in TABLE 2 and TABLE 3. FIG. 3 illustrates how aconventional 9 bit A/D converter is sufficient to provide a 17 bitdigital output by incorporating an 8 bit digital unscaling unit 64 thatoperates on every sensor pixel. A multiplexer 66, in FIG. 3, generatesoutputs signals from each sensor's pixel(TN,j) into an A/D converted 62which digitizes each pixel's analog output with 9 bit. The 9 bit A/Dconverter 62 output is digitally unscaled with the digital unscalingunit 64 according to a sensor pixel's scale tag G(TN,j), whichrepresents the scaling factor that each sensor pixel has received. FIG.4 shows a block diagram of an example register that illustrates howdigital unscaling is incorporated with the 9 bit A/D, for various scaleranges. Here, the digital unscaling arithmetic unit acts as a divider toremove the effects of scaling (1×, 4×, 16×, 64×, or 256×) applied toeach sensor pixel's to equalize the S/N ratio within approximately 2×.This is facilitated by carrying each “sensor pixel's” scale factor tagrepresenting each sensor pixel's amplitude and the same tag providesinformation that is needed to perform a sensor pixel's unscaling.

The A/D architecture shown in FIGS. 3-4 is designed to provide a 17 bitdigital output with a nine bit A/D converter coupled to an 8 bit digitalunscaling unit. A nine bit A/D converter is suitable because it maps,within five signal ranges, the location of each A/D converter's signal,represented in column 6, TABLE 3, and it is mapped with an instantaneousS/N range that is less than 9 bits. Additionally, this mappingsimplifies defining the A/D converter's LSB since in this example it isequal to 30 electrons. Thus each sensor pixel can be digitized with anine bit A/D, while preserving the improved S/N ratios. This digitaltransformation is completed by digitally unscaling each sensor pixel's 9bit digital signal with, for example, an 8 bit scale tag assigned toeach sensor pixel. The scale tag assigned to each sensor pixelrepresents the scale factor (1×, 4×, 16×, 64×, or 256×) used to equalizethe S/N ratio by mapping five Signal Ranges into one. Division by themodulo “2” sensor pixel's scale tag is readily performed by shifting the9 bit A/D output down into a 17 bit output register. The 9 bit sensorpixel's output is shifted to the left based on sensor pixel's scale tag,as is illustrated in FIG. 4.

This digital transformation technique presented applies to focal planesensor intended for scanning systems imaging high dynamic range scenes.It applies to imaging focal plane sensor using quantum detectorsoperating in different spectral bands, including: UV, visible, SWIR,MWIR, and LWIR. However, the embodiment of the digital transformationdepends on the focal plane sensor's operating spectral band.

FIG. 5 illustrates an example of object space (or scene) 82 imaged withscanning operation 80. The object space 82 is scanned via an oscillatingmirror 86 and scans the object space image across an array of imagingcolumns 84 (only one is shown) containing TDI segments, where each TDIsegments may have a different number of TDI stages. In the forward scandirection the object space 82 is scanned with a mirror fromleft-to-right. Such a scan produced an image of the object space withinthe TDI column 96. The image produced in the TDI column 96 movessynchronously with the scanned image by adjusting the speed of theTDI-CCD transfer clocks. In the reverse scan direction, the object scene82 is scanned from right-to-left and moves synchronously with image ofobject space within the TDI column 96. Movement of the object spaceimage within the TDI column is controlled by the speed of the TDI-CCDtransfer clocks.

A PI/SO CCD R/O register 88 is located at a first end of the imagingcolumn 84 and a second PI/SO CCD R/O register 90 is located at a secondend of the imaging column. Both are used for reading out the sensorpixel signal formed in a TDI-CCD imaging columns 96 (only one columnshown). In forward scan, each sensor pixel's brightness is readout withthe left CCD R/O register 88 and this provides advanced knowledge ofeach sensor pixel's brightness. This knowledge determines how many TDIstages are applied to each sensor pixel to equalize the inter sensorpixel S/N ratio within 2×, approximately. The image is readout with theCCD R/O register 90 on the right. In reverse scan, the right CCD R/Oregister 90 is used for reading out advanced knowledge of each sensorpixel's brightness. This knowledge determines how many TDI stages areapplied to each sensor pixel to equalize the inter sensor pixel S/Nratio within 2×, approximately. The image is readout with the CCD R/Oregister 88, on the left.

Advanced knowledge of each sensor pixel's photosignal is obtained byreading a single TDI sensing stage 92 and 94 on the left and right sidesof the TDI imaging column 96, as illustrated in FIG. 5. The single TDIsensing stages are on the left and right sides of the TDI imaging column96 (and next to each R/O PI/SO register 88 and 90) and are clockedindependently of the TDI imaging column 96. In a forward scan operation,the object space image is first scanned across the left single TDIsensing stage 92 before it is scanned over and imaged with the remainingTDI stages on the right. In the forward scan, the object space image isRead/Out with the R/O PI/SO register 90 on the right. In reversescanning sequence, the image is first scanned across the right singleTDI sensing stage 94 before it is scanned and imaged with the remainingTDI stages on the left. In the reverse scan, the right single TDIsensing stage 94 is Read/Out with the R/O PI/SO register 90 on theright. In a reverse scan, the object space image is scanned over andimaged with the remaining TDI stages on the left. In reverse scan, theobject space image is Read/Out with PI/SO registers 88, located on theleft. Given the image scanning sequence in both directions, Read/Out ofthe single TDI sensing stage (containing each sensor pixel's photosignalamplitude) occurs before object space is imaged with the TDI columns andRead/Out. Thus, the scanning sequence in each direction insures thatsufficient advanced knowledge of each sensor pixel's photosignal valueis available to allow time for adjusting the number of TDI stages pereach sensor pixel.

Advance knowledge of each sensor pixel's photosignal can be obtainedwith improved sensitivity by using the approach shown in FIG. 6. FIG. 6illustrates another example of object space (or scene) 102 imaged withscanning operation 100. As illustrated in FIG. 6, an object space 102 isscanned with an oscillating mirror 106 and produces an image of theobject space across an array of imaging columns 104 (only one is shownwithout detectors) containing TDI segments, where each TDI segments mayhave a different number of TDI stages. In the forward scan direction,the object space (or scene) 102 is scanned with a mirror fromleft-to-right. Such a scan produces an image of the object space withinthe TDI column 116. The image produced within the TDI column 116 movessynchronously with the scanned image by adjusting the TDI-CCD transferclocks. In the reverse scan direction, the object space (or scene) 102is scanned from right-to-left and moves synchronously with the objectspace image within the TDI column 116. Movement of the object spaceimage within the TDI-column is controlled by the TDI-CCD transferclocks. A PI/SO CCD R/O register 108 is located at a first end of theimaging column 104 and a second PI/SO CCD R/O register 110 is located ata second end of the imaging column 104 and these are used for readingout the sensor pixel signal formed in a TDI-CCD imaging columns 116(only one is shown).

In forward scan, the left CCD R/O register 108 is used for readout ofeach sensor pixel's brightness signal 112 to provide advanced knowledgeof each sensor pixel's brightness value. This information is used todetermine how many TDI stages are applied to each sensor pixel toequalize the inter sensor pixels' S/N ratio within 2×, approximately.The object space is imaged with the TDI-CCD imaging column locatedbetween the two R/Os 108, and 110, and is readout with the CCD R/Oregister 110 on the right In reverse scan, the right CCD R/O register110 is used for readout of each sensor pixel's brightness signal 114 toprovide advanced knowledge of each sensor pixel's brightness value. Thisinformation is used to determine how many TDI stages are applied to eachsensor pixel to equalize the inter sensor pixels' S/N ratio within 2×,approximately. The object space is imaged with the TDI-CCD imagingcolumn located between the two Read/Outs 108, and 110 and is readoutwith the CCD R/O register 108 on the left.

For forward scan, 4 TDI sensing stages 112 are placed on the left sideof the left R/O PI/SO CCD register 108. For reverse scan, 4 TDI sensingstages 114 are placed on the right side of the right R/O PI/SO CCDregister 110. Such placement provides room for several TDI sensingstages and TDI scanning compatibility. It is to be appreciated that theR/O PI/SO CCD registers 108 and 110, shown in FIG. 6 need to be designedto accept charge signals from two sides instead of just one side.Specifically, in forward scan, the 4 TDI sensing stages 112 injectssignal charge from the left into R/O PI/SO CCD register 108.Concurrently, in forward scan the TDI image charge signals (formed inthe column with several TDI segments) are injected into the left side ofthe R/O PI/SO CCD register 110. Specifically, in reverse scan, the 4 TDIsensing stages 114 inject signal charge from into right into the R/OPI/SO CCD register 110. Concurrently, in reverse scan the TDI imagecharge signals (formed in the column with several TDI segments) areinjected into the right side of the R/O PI/SO CCD register 108.

The advanced knowledge sensing stages' information on each sensorpixel's photosignal is used for calculating the number of TDI stagesapplied to each sensor pixel. Adjusting the number of TDI per sensorpixel can be implemented by including in each TDI-CCD imaging column twotypes of antiblooming drains. One type of antiblooming drain can beincorporated in every one or other TDI stage in the imaging columns.This type of antiblooming stage has a global antiblooming leveladjustment which prevents signal charge blooming when imaging largedynamic range scene. A second type of antiblooming stage in the TDI-CCDimaging column is called a digital blooming stage, or DBD.

The digital blooming stage has two operating modes: (1) it can functionas a regular antiblooming stage, and (2) or, if directed, it can emptythe signal charge contained within a given TDI-CCD stage. Thus, a sensorpixel's signal charge which accumulates as the sensor pixel's signal isshifted down the TDI-CCD imaging column can be reset to zero by avoltage pulse applied to the digital blooming stage located wherein thesensor pixel's signal charge is located. Thus, the number of TDI stagesthe sensor pixel's charge receives is limited to the number of TDI-CCDstages remaining in a column before the sensor pixel's charge istransferred into the R/O PI/SO CCD registers used for reading out theobject space image obtained with the TDI-CCD column. The terms“blooming” and “antiblooming” are deemed synonymous throughout thisdocument.

Eight digital antiblooming stages are shown in the TDI imaging column116 of FIG. 6. For the forward scan direction, four digital antibloomingdrains are located on the right side of the TDI imaging column 116. Forthe reverse scan direction, four digital antiblooming drains are locatedon the left side of the TDI imaging column 116. Thus eight digitalantiblooming drains are located within the nine TDI segments and aresymmetrically inserted within each TDI imaging column. The number ofTDIs a sensor pixel receives is varied according to which digitalantiblooming drain stages are addressed as a sensor pixel traverseswithin the 256 stage TDI column during imaging.

In the example of FIG. 6, a sensor pixel receives 256 TDI if none of theforward (reverse) digital antiblooming drains are addressed as a sensorpixel moves in the forward (reverse) scan direction within the 256 stageTDI imaging column. A sensor pixel receives 64 TDI if only digitalantiblooming drain forward (reverse) 64 DBD is addressed as a sensorpixel moves the forward (reverse) scan direction within the 256 stageTDI imaging column. A sensor pixel receives 16 TDI if only digitalantiblooming drain 16 DBD forward (reverse) is addressed as a sensorpixel moves in the forward (reverse) scan direction within the 256 stageTDI imaging column. A sensor pixel receives 4 TDI if only digitalantiblooming drain 4 DBD forward (reverse) is addressed as a sensorpixel moves in the forward (reverse) scan direction within the 256 stageTDI imaging column. A sensor pixel receives 1 TDI if only digitalantiblooming drain 1 DBD forward (reverse) is addressed as a sensorpixel moves in the forward (reverse) scan direction within the 256 stageTDI imaging column.

Each digital blooming drain stages are located within each TDI columnand are individually addressed by a digital voltage pulse or resetpulse. When the digital blooming drain stage is addressed by a digitalvoltage pulse, the charge signal of a sensor pixel located within theTDI stage with digital blooming drain is reset to zero. If the digitalblooming drain stage is not addressed, the sensor pixel's charge signalis incremented by one TDI. Thus, the number of TDI stages a sensor pixelreceives depends on the action of the digital blooming drain stages onthe sensor pixel's signal. In the forward (reverse) scan, a sensor pixelis transferred within the 256 stage imaging TDI column and the number ofTDI it receives depends by which of digital blooming drain on the right(left) side reset it's the signal charge. If a sensor pixel's signalcharge is not reset as it is transferred in the 256 stage long TDIcolumn, it will receive 256 TDIs. If a sensor pixel's charge signal inthe forward (reverse) scan is reset by the right (left) side digitalblooming drains (64 DBD, 16 DBD, 4 DBD, or 1 DBD) it will receive,respectively, (64TDI, 16TDI, 4TDI, or 1TDI).

FIG. 7 illustrates an example block diagram of a four phase TDI cell 130representing a TDI stage. The TDI cell 130 size can be about 20 μm×20 μmfor use with a SWIR, MWIR, or LWIR photodetectors. The TDI cell 130 caninclude a 10 μm wide by 20 μm long four phase TDI-CCD shift registerstage 132. The signal from a photodetector is electrically injected intoa direct injection source 134, and flows under a direct injection gate136 into an integration well 138. Photocharge integrated in theintegration well is limited by a blooming gate 140, which double as areset gate when this structure functions as a digital blooming drain andremoves all the charge from the integration well 138 into a bloomingdrain 142. Photocharge can be injected from the integration well 138into the TDI-CCD shift register stage 132 by action of a chargeinjection gate 144. Photocharge can be moved between different TDIstages with the TDI-CCD shift register stage 132 by clocking the TDI-CCDshift register phases with clock signals.

Each photodetector has a terminal common with all the photodetectors inan array and a second isolated terminal which is electrically connectedto the DI source 134, shown in FIG. 7. Injected photosignal flows underthe DI gate 136 into an integration well 138. Photosignal is integratedin the integration well 138 defined by channel stops 146, and theconfining voltage potentials applied to the integration well 138, theblooming & reset gate 140, the DI gate 136 and the charge injection gate144. Antiblooming is achieved by adjusting the blocking voltage appliedto the blooming & reset gate 140 and thereby limiting how much chargecan be integrated in the integration well 138. The potential of chargesintegrated in the integration well 138 increases as charge builds-upuntil it equals to the potential barrier formed by the blooming & resetgate 140. Any additional charge injected into the integration well 138is no longer confined and flows under the blooming & reset gate 140 intothe blooming drain 142. The blooming drain 142 is connected to apotential which attracts the charge flowing under the blooming & resetgate 140. This prevents charge blooming from the integration well 138into the TDI-CCD register 132. Similarly, charge in the TDI-CCD register132 is prevented from blooming by adjusting the blocking potentialapplied to the charge injection gate 144 to be less blocking than theblocking potential applied to the 4 Phase TDI-CCD register 132.

Digital Antiblooming can be used to remove all the charge from theintegration well 138 and the potential well of the 4 Phase TDI-CCDregister 132 located next to the charge injection gate 144. This isachieved by applying a non-blocking potential to the blooming & resetgate 140 and the charge injection gate 144. This drains all the chargeinto the blooming drain 142 and determines the number of TDIs applied toa sensor pixel. After the charge removal, the potential applied to thecharge injection gate 144 and blooming & reset gate 140 are biased intotheir antiblooming levels. Charge Injection from the integration well138 into a potential well inside the 4 Phase TDI-CCD register 132 isperformed by applying a non-blocking potential to the charge injectiongate 144, and making the integration well 138 less attractive to promotecharge flow from the integration well 138 into the 4 Phase TDI-CCD well.After the charge is injected from the integration well 138, the chargeinjection gate 144 is biased into its normal blocking potential.

The digital transformation approach is valid for imaging large dynamicrange scenes in different spectral bands, including: UV, Visible, SWIR,MWIR and LWIR FPAs. Because of maturity differences in detector materialtechnology, the optimal FPA configuration/architecture approach dependson the spectral band selected. However, unlike the detector materials,silicon is the preferred material for focal plane signal processingsignal in terms of maturity, cost, and performance. Thus, silicon is thelikely material of choice for fabricating a Read Out Integrated Circuit(ROIC) for the different spectral band bands, provided adjustments aremade for the detector material maturity.

FIG. 8 illustrates an example of an imaging focal plane sensor 150formed from a back side imaging (BSI) bidirectional scan TDI-CCD FocalPlane Array 152 bonded to a silicon ROIC 154. Bonding between UV orVisible TDI-CCD FPA and ROIC can employ Indium Bump Bonding or WaferBonding. For maximum fill factor, the UV or Visible photodetector arraysare AR coated to operate in a Back Side Imaging configuration. The focalplane sensor features variable TDI for each sensor pixel to achievemaximum sensitivity by equalizing the inter sensor pixels' S/N ratiowithin 2×, approximately. Silicon UV and Visible scanning sensorsimaging high dynamic range scenes potentially offer the lowest cost andbest performance. Silicon photodetectors absorbs UV and Visible photons.Thus, the UV and Visible photodetector and ROIC can be made in silicon.This leads to better sensitivity since integrating the photodetectorsand the TDI-CCD processors avoids electrical injection noise andreplacing it with directly photogenerating charge signals within theTDI-CCD potential wells. Thermal expansion mismatch issues are alsoavoided by making the focal plane sensor TDI-CCD and the ROIC insilicon.

FIG. 9 illustrates an example of an imaging focal plane sensor 170formed from a SWIR, or MWIR, or LWIR, photodetector FPAs 172 connectedto a ROIC 174. For maximum fill factor, the SWIR or MWIR, or LWRIphotodetector FPA 172 is AR coated and operates in Back-Side-Imagingmode. The SWIR, or MWIR, or LWIR ROIC 174 features variable TDI per eachsensor pixel and electrical interface circuits between eachphotodetector and ROIC. Intrinsic SWIR, MWIR or LWIR photodetectors aretypically made in InGaAs (for SWIR) InSb or HgCdTe (for MWIR) and HgCdTe(for LWIR). The technology in these materials is not sufficientlydeveloped to make high quality TDI-CCD, which would allow integration ofthe photodetectors with the TDI-CCD processor. Hence, signals from suchphotodetectors are electrically (not optically as with UV and Visiblephotons) injected into a silicon TDI-CCD with a special injectionstructure and this requires electrical connection between ROIC and eachphotodetector, as is illustrated in FIG. 9.

Direct Injection is the simplest electrical coupling structure betweenphotodetector and TDI-CCD. More complicated electrical couplingstructures, like buffered direct injection and transimpedance amplifier,can be used to obtain better injection performance. Thus, the sensorfocal plane architecture of SWIR, or MWIR or LWIR is significantlyimpacted since all the signal processing has to be performed in theSilicon ROIC. Each photodetector in a SWIR, or MWIR or LWIR array 172 iselectrically connected to an injection structure with bump bonding ordirect wafer bonding to the ROIC 174, which includes a TDI-CCDprocessor, and electrical injection structures. The high densityinterconnections between photodetectors and ROIC are consistent withexisting bump bonding or wafer bonding technology. However, theelectrical interface between each photodetector and TDI-CCD addinjection noise and this may impact performance at the lowest signallevels.

The ROIC 174 for SWIR, or MWIR, or LWIR photodetector arrays includes:electrical interface to each detector, digital antiblooming drainstages, regular antiblooming drain stages, TDI-CCD stages, CMOS A/Dconverter, X-Y address stages, and Read Out circuits. Integrating thesefunctions is possible with high density silicon lithography, and this ispartly mitigated because the diffraction limit for SWIR, MWIR and LWIRis larger than for UV and Visible. Hence the sensor pixel's foot printfor SWIR, MWIR and LWIR photodetectors is at least 2× larger than thesensor pixel's size for UV and Visible photodetectors. As a result, moreroom is available for integrating: the electrical coupling circuitbetween each photodetector and the ROIC 174, the digital antibloomingdrains, the regular digital antiblooming drains, and the TDI-CCDregisters. The readout circuits, the CMOS A/D converter and the drivefor the X-Y address circuits are not located within the sensor pixelarea hence they do not significantly impact the ROIC's circuit densityrequirements. The increased circuit density requirement is compatiblewith existing CMOS circuit densities.

What has been described above includes exemplary implementations of thepresent invention. It is, of course, not possible to describe everyconceivable combination of components or methodologies for purposes ofdescribing the present invention, but one of ordinary skill in the artwill recognize that many further combinations and permutations of thepresent invention are possible. Accordingly, the present invention isintended to embrace all such alterations, modifications, and variations.

What is claimed is:
 1. A scanning focal plane sensor for an imagingsystem comprising: a M×N time delay integration (TDI) imaging chargecoupled device (CCD), where M is a number of sensor pixels and N is anumber of TDI stages per sensor pixel, and M and N are integers greaterthan one; and an imaging controller configured to determine an initialphotosignal value for each sensor pixel based on an initial capture ofan image of an object scene, and select a number of TDI stages forintegrating charge of each respective sensor pixel of the image based onits respective initial photosignal value.
 2. The focal plane sensor ofclaim 1, wherein the imaging controller determines a scale factor foreach sensor pixel, based on the initial photosignal value, that scaleseach initial photosignal value into a same photosignal value range, thescale factor determines the number of TDI stages selected forintegrating charge of each sensor pixel.
 3. The focal plane sensor ofclaim 2, further comprising a readout circuit that converts eachintegrated charge into an analog voltage and an analog/digital converterthat digitizes each analog voltage to provide a digitized sensor pixelphotosignal value for each sensor pixel, the digitized sensor pixelphotosignal value for each sensor pixel being unscaled by its respectivescale factor to recover its initial photosignal value, while maintaininga signal to noise ratio that is approximately within approximately afactor of 2 for each sensor pixel.
 4. The focal plane sensor of claim 3,wherein the analog/digital converter outputs an X bit word representingthe scaled digitized sensor pixel's photosignal value into a Y bitregister, where X and Y are integers greater than one and Y is greaterthan X, wherein the bits of the register are shifted to performunscaling based on the scale factor associated with a given sensor pixelto recover its initial photosignal value.
 5. The focal plane sensor ofclaim 2, wherein initial photosignal values fall within one of aplurality of photosignal value ranges, where each sensor pixel's scalefactor scales its initial photosignal value into a brightest photosignalvalue range of the plurality of photosignal value ranges.
 6. The focalplane sensor of claim 1, further comprising M×K sensing stages, where Kis an integer equal to or greater than one, from where the imagingcontroller obtains the initial photosignal value from a sensing stageassociated with a given sensor pixel for each sensor pixel.
 7. The focalplane sensor of claim 6, further comprising a parallel-in/serial out(PI/SO) CCD multiplexer that multiplexes integrated charge of eachrespective sensor pixel to a readout circuit that converts eachintegrated charge into an analog voltage and an analog/digital converterthat digitizes each analog voltage to provide a digitized representationof each sensor pixel photosignal value, the digitized representation ofeach sensor pixel photosignal value being digitally unscaled by itsrespective scale factor to recover its initial photosignal value, whilemaintaining a signal to noise ratio that is within approximately afactor of 2 for each sensor pixel.
 8. The focal plane sensor of claim 1,wherein each TDI stage comprises a TDI cell that integrates charge froma photodetector in an integration well and injects the charge into aTDI-CCD well, the charge in the TDI-CCD well is integrated with chargeaccumulated from previous TDI-CCD stages, each TDI cell furthercomprises a reset gate that removes the charge from the integration welland the TDI-CCD well in response to a reset control signal, the imagingcontroller selecting a number of TDI stages by providing a reset controlsignal to a TDI stage that is prior to the selected TDI stages.
 9. Thefocal plane sensor of claim 8, wherein the reset gate is a digitalblooming (DBD) and reset gate associated with each sensor pixel, andfurther comprising M×H DBD control reset signals coupled to H selectedTDI stages out of the N TDI stages in a column for each sensor pixel todefine a plurality of TDI segments that when selected provide respectiveintegration times by resetting one or more TDI stages in one or moreprevious TDI segments that allow for scaling of initial photosignalvalues into a same photosignal value range for each of the M sensorpixels, where H is an integer greater than or equal to one.
 10. Thefocal plane sensor of claim 1, wherein the M×N TDI imaging CCD is focalplane array that is wafer bonded to a silicon read out integratedcircuit (ROIC) that includes the imaging controller.
 11. The focal planesensor of claim 1, wherein the M×N infrared (IR) photodetector arraythat is wafer bonded or bump bonded to a read out integrated circuit(ROIC) that includes a M×N TDI imaging CCD and the imaging controller.12. The focal plane sensor of claim 1, wherein the M×N TDI imaging CCDis a bidirectional imaging CCD.
 13. A scanning imaging focal planesensor configured to perform a forward and a reverse scan operation, thefocal plane sensor comprising: a bidirectional M×N time delayintegration (TDI) imaging charge coupled device (CCD), with one detectorconnected to each TDI stage, where M is a number of columns, and N is anumber of TDI stages in each column used to scale the integration timeper each sensor pixel, and M and N are integers greater than one; M×Ksensing stages, where K is an integer greater than one, wherein a firstset of sensing stages for each of the M sensor pixels resides on a firstside of the bidirectional M×N TDI imaging CCD and a second set ofsensing stages for each of the M sensor pixels resides on a second sideof the bidirectional M×N TDI imaging CCD; and an imaging controllerconfigured to determine an initial photosignal value for each sensorpixel based on an initial capture of an image of an object space (orscene) from the first sensing stages during a forward scan, and todetermine an initial photosignal value for each sensor pixel based on aninitial capture of an image of an object scene from the second sensingstages during a reverse scan, the imaging controller selecting a numberof TDI stages for integrating charge of each respective sensor pixel forthe respective image based on its respective initial photosignal value.14. The focal plane sensor of claim 13, wherein the imaging controllerdetermines a scale factor for each sensor pixel, based on the initialphotosignal value, that scales each initial photosignal value into asame photosignal value range, the scale factor determines the number ofTDI stages selected for integrating charge of each sensor pixel.
 15. Thefocal plane sensor of claim 13, further comprising a firstparallel-in/serial out (PI/SO) CCD multiplexer that resides on a firstside of the bidirectional M×N TDI imaging CCD and a second PI/SO CCDmultiplexer that resides on a second side of the bidirectional M×N TDIimaging CCD, the first multiplexer multiplexes integrated charge fromthe first set of sensing stages for each sensor pixel to a first readoutcircuit, and the second multiplexer multiplexes integrated charge fromthe selected TDI stages for each sensor pixel to a second readoutcircuit during a forward scan operation, and the second multiplexermultiplexes integrated charge from the second set of sensing stages foreach sensor pixel to the second readout circuit, and the firstmultiplexer multiplexes integrated charge from the selected TDI stagesfor each sensor pixel to the readout circuit during a reverse scanoperation.
 16. The focal plane sensor of claim 15, wherein the first setof sensing stages resides between the first PI/SO CCD multiplexer andthe first side of the bidirectional M×N TDI imaging CCD and the secondset of sensing stages resides between the second PI/SO CCD multiplexerand the second side of the bidirectional M×N TDI imaging CCD.
 17. Thefocal plane sensor of claim 16, wherein the first PI/SO CCD multiplexerresides between the first set of sensing stages and the first side ofthe bidirectional M×N TDI imaging CCD and the second PI/SO CCDmultiplexer resides between the second set of sensing stages and thebidirectional M×N TDI imaging CCD, the first and second PI/SO CCDmultiplexers being configured to accept inputs from both the sensingstages on one side and the bidirectional M×N TDI imaging CCD on theopposite side.
 18. The focal plane sensor of claim 15, wherein the firstreadout circuit converts the integrated charge to an analog voltage andprovides the analog voltage to a first analog/digital converter thatdigitizes each analog voltage to provide a digitized sensor pixelphotosignal value for each sensor pixel, and the second readout circuitconverts the integrated charge to an analog voltage and provides theanalog voltage to a second analog/digital converter that digitizes eachanalog voltage to provide a digitized sensor pixel photosignal value foreach sensor pixel, the digitized sensor pixel photosignal value for eachsensor pixel being unscaled by its respective scale factor to recoverits initial photosignal value, while maintaining a signal to noise ratiothat is within a factor of approximately 2 for each sensor pixel. 19.The focal plane sensor of claim 18, wherein each of the first and secondanalog/digital converter outputs an X bit word representing thedigitized sensor pixel photosignal value of a sensor pixel into a Y bitregister, where X and Y are integers greater than one and Y is greaterthan X, wherein the bits of the register are shifted during theunscaling based on the scale factor associated with a given sensor pixelto recover its initial photosignal value.
 20. The focal plane sensor ofclaim 13, wherein each TDI stage comprises a TDI cell that integratescharge from a photodetector in an integration well and injects thecharge into a TDI-CCD well, the charge in the TDI-CCD well is integratedwith charge accumulated from previous TDI-CCD stages, each TDI cellfurther comprises a reset gate that removes the charge from theintegration well and the TDI-CCD well in response to a reset controlsignal, the imaging controller selecting a number of TDI stages byproviding a reset control signal to a TDI stage that is prior to theselected TDI stages.
 21. The focal plane sensor of claim 20, wherein thereset gate is a digital blooming (DBD) and reset gate associated witheach sensor pixel, and further comprising a first and second set of M×HDBD control reset signals coupled to H selected TDI stages in eachcolumn with N TDI stages for each sensor pixel to define a plurality ofTDI segments that when selected provide respective integration times byresetting one or more TDI stages of one or more previous TDI segmentsthat allow for scaling of initial photosignal values into a samephotosignal value range for each of the M sensor pixels, where H is aninteger greater than or equal to one, the first set of M×H DBD controlreset signals being employed during a reverse scan operation, and thesecond set of M×H DBD control reset signals being employed during aforward scan operation.
 22. A method for image capturing of an objectspace by a scanning imaging focal plane sensor, the method comprising:determining an initial photosignal value for each of a plurality ofsensor pixels based on an initial capture of an image of an objectscene; determining a scale factor for each sensor pixel to increase theintegration time for each sensor pixel to scale each sensor pixel'sphotosignal value into a value that falls within a predetermined sensorpixel signal range; and adjusting the integrating time of each sensorpixel of the image by a number of time delay integration (TDI) stagescorresponding to its determined scale factor to equalize each of thesensor pixel values within the predetermined sensor pixel signal rangeand provide a signal to noise ratio for each of plurality of sensorpixels that is within a factor of
 2. 23. The method of claim 22, furthercomprising: converting the integrated charge to an analog sensor pixelvalue for each of the plurality of sensor pixels; digitizing the analogscaled values into digitized sensor pixel values for each of theplurality of sensor pixels; and unscaling each digitized sensor pixelvalue by its respective scale factor for each of the plurality of sensorpixels to recover each sensor pixel's initial photosignal value.
 24. Themethod of claim 23, wherein each initial photosignal value falls withinone of a plurality of photosignal value ranges, where each sensorpixel's scale factor scales its initial photosignal value into abrightest photosignal value range of the plurality of photosignal valueranges.